Adjustable spike nozzle for thrust motors



April 7, 1970 K. c. WILSON 3,504,860

ADJUSTABLE SPIKE NOZZLE FOR THRUST MOTORS MOVABLE COWL (BALANCED FORCESFiled- July 7, 1964 l6 FIXED COWL.

FIG. IB. (PRIOR ART) 23 s2 4 64 70 Ml FlG. 3.

66 I I y 44 1, M INVENTOR. 28 4 38a, V KENNETH 0. WILSON FIG. 4 BY (4.ATTORNEY.

United States Patent 3 504 86 ADJUSTABLE SPIK E N OZZLE FOR THRUSTMOTORS Kenneth C. Wilson, Cumberland, Md., assignor, by mesneassignments, to the United States of America as represented by theSecretary of the Navy Filed July 7, 1964, Ser. No. 380,962 Int. Cl. B63h11/10 US. Cl. 239-26519 3 Claims This invention relates to jetpropulsion motors and more particularly to improvements in adjustablearea exhaust nozzles for use with such motors.

In the art of jet propulsion, it is well known practice to vary the areaof an exhaust thrust nozzle, with change of altitude of the vehiclebeing propelled by a thrust motor, to thereby compensate for the changein atmospheric back pressure and control the motor thrust in such mannerthat the motor operates at optimum efiiciency under all conditions ofback pressure. Motors of this type have been constructed to operateclose to the ideal isentropic process in which entropy remains constantwith a change in enthalpy. Such type of process is described in GasTurbines for Aircraft, by Driggs and Lancaster, published by the RonaldPress Company, New York, 1955, pages 32 and 33.

FIGS. 1A and 1B of the accompanying drawing illustrate isentropic spikenozzles of the type referred to. In FIG. 1A the rear end of the thrustmotor is provided with a fixed spike and the area of the exhaust annulusis varied by positioning the movable cowl. In FIG. 1B the cowl is fixedand the area of the exhaust annulus is varied by positioning the movablespike. In the FIG. 1A system the axial gas forces on the cowl arebalanced (F =F which is an advantage, since the movement of the cowl canbe effected with a small actuating force. One of its disadvantages,however, is that the cowl occupies space outside of the motor thusincreasing weight and bulk to the overall system. In the FIG. 1B systemthe foregoing disadvantage is obviated but the motor gas pressure isapplied to substantially the entire cross section of the spike thuscreating a high unbalanced force tending to move the spike toward closedposition. The spike support must thus be of adequate strength towithstand such unbalanced force. As will also be apparent, highactuating force is necessary to move the spike to a desired position.Both systems also have the disadvantage of moving parts which aresubjected to high temperature gases and deposits which may hinder theirmovement.

Among the general objects of the invention are the provision of amovable spike nozzle which obviates the disadvantages of the prior art,above referred to.

Other, and more specific objects, are the provision of a movable spikenozzle which, as compared to the prior art devices, reduces stresses,reduces weight, reduces spatial requirements to thereby permit increasedvolume for the motor propellant and increases reliability.

A further object is the provision of a movable spike nozzle which issubstantially balanced by the gas forces, thus requiring a relativelysmall actuating force for positioning it.

A further object is the provision of a movable spike nozzle whichpermits increased expansion ratios within equivalent or less spatialrequirements of the prior art.

A further object is the provision of spike actuating apparatus which isdisposed within the spike, thus utilizing a heretofore unused space.

A further object is to decrease the mass of movable nozzle parts, tothus reduce their inertia effects, and permit more rapid movement withminimized actuating force.

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Still further objects, advantages, and salient features wlll become moreapparent from the description to follow, the appended claims and theaccompanying drawing, in which:

FIGS. 1A and 1B are cross sections of prior art;

FIG. 1 is a broken away side elevation of an exemplary form of theinvention;

FIG. 2 is a section taken on line 22, FIG. 1;

FIG. 3 is an enlarged section taken on line 33, FIG. 2; and

FIG. 4 is a cross section of an alternative form of a component of theinvention.

Referring now to the drawing, an exemplary environment of the inventionis illustrated in FIGS. 1 and 2 in which any conventional thrust motor10 is provided with a combustion chamber 12, containing a solidpropellant (not shown), the rear end of the motor terminating in aninwardly curved cowl 14 within which a movable spike 16 is disposed,thus providing a variable area annular discharge orifice 18.

Referring now to FIG. 3, spike 16 comprises an outer shell 20 ofgraphite, having threads 22 which engage corresponding threads on aspike shell insulator 23 composed of Spauldite. The outer shell andinsulator are otherwise secured together by a member 24 which threadedlyengages the insulator, provided with a shoulder or flange 216 whichengages the rear end of the outer shell. This member is preferably anasbestos phenolic material. Angularly spaced vents 27 are provided tobleed off gases produced by the charring of phenolic insulator 23.

An aluminum support tube 28 is secured at its forward end to the frontbulkhead 29 of the combustion chamber, the tube being covered with aninsulating material 30, also preferably of Spauldite. A frusto-conicalaluminum pressure plate 33 is disposed on the rear end of the tube, itsexposed surface being covered by an insulator plate 34-, the pressureplate and insulator plate being secured in position by a nut 3-6,disposed on an actuator 38, the nut threadedly engaging the rear end oftube 28. O-rings 40, 42, prevent leakage of gas from the combustionchamber.

The outer edge of insulator 34 is provided with a cylindrical flange 44which telescopes within an asbestos phenolic ring 46 of U-shaped crosssection, the outer surface of the ring threadedly engaging a graphitespike spacer 48 having a plurality of webs 50, the outer ends of thewebs terminating in a two part ring 52 which is secured to cowl 14in anydesired manner. As shown, this comprises an asbestos phenolic ring 54and a covering aluminum ring 56, secured to the cowl by a snap ring 58.

The forward end of ring 46 is provided with a plurality of angularlyspaced apertures 60 which permit gas pressure to be applied to theforward face 62 of shell 20 and the forward face 64 of insulator 23. Aswill be apparent, the total area of these two faces is a smallproportion of the total cross section of the spike. The spike is thusurged rearwardly with a force equal to the combustion chamber pressuretimes the area of these two faces as illustrated by rearwardly directedarrows. The spike is urged in the opposite direction by pressure of thegas downstream of nozzle 18, acting on the entire cross section of thespike, as illustrated by forwardly directed arrows. While this area isconsiderably in excess of the area of faces 62, 64 the pressure isconsiderably less than combustion chamber pressure. As will now beapparent, the force tending to move the spike in a desired direction maybe controlled by suitably proportioning the area of faces 62, 64 to thespike cross section if the combustion chamber pressure and pressure onthe rear side of shell 20 are known. In the preferred embodiment, thearea of faces 62, 64 is so chosen to provide a force tending to move thespike in a rearward direction.

Actuator 38 may be of any suitable type such as an electric motor or apiston which is actuated by fluid pressure, either gas or hydraulic. Ifelectric, control wires may extend through tube 28 to suitable controlapparatus in the motor and if actuated by fluid pressure, the pressuremay be applied through the tube. In either construction, a reciprocableactuator rod 66, affixed at one end to member 24, is provided which maycontrol the position of the spike. In one embodiment, the actuator maybe considered as a single action piston in which the control force isadditive to the force of the exhausting gases. Thus, the rearward forceon faces 62, 64 would be slightly in excess of the forward forces on theentire spike cross section, tending to move the spike toward a smallerthroat aperture, and the force applied to the actuator, when movement isdesired, would be slightly in excess of the difference between therearward and forward gas forces.

FIG. 4 illustrates another form of actuator wherein a double actingpiston 68 may be moved in opposite directions by selective applicationof fluid pressure through tube 28 and a separate conduit 70. Thisconstruction may be preferable in motors which require very rapidmovement of the spike, such as in motors in which it is desirable toterminate burning of the propellant by rapidly moving the spike to amaximum nozzle opening position thereby interrupting propellantcombustion.

What is claimed is:

1. In a variable throat area convergent-diveregnt nozzle of theisentropic spike type for use with a gaseous thrust motor having a cowlmember fixed to the rear end of the motor and having an annular surfaceforming the outer wall of the convergent portion of the nozzle andterminating in a circular opening at the throat of the nozzle, acircular spike member movable axially relative to said opening having afirst portion forming the inner wall of the convergent portion of thenozzle and a second downstream portion forming the inner wall of thedivergent portion of the nozzle, said inner wall of the convergent anddivergent portions being subjected to pressure of the gas, producing afirst force tending to move the spike member forwardly to increase thearea of the throat, the improvements, in combination, comprising:

(a) said spike member having a cylindrical tubular portion slideablydisposed within a stationary tubular cylinder and having an annular endsurface of considerably less area than the projected area of saidconvergent-divergent portions, said cylinder communicating with saidchamber, to produce a second force tending to move the spike memberrearwardly to thereby decrease the area of the throat,

(b) and an actuator disposed within said spike member and operativelyconnected thereto, so constructed to produce a force in excess of thedifference between said first and second forces, to thereby move thespike member to a desired axial position.

2. In a variable throat area convergent-divergent nozzle of theisentropic spike type for use with a gaseous thrust motor having a cowlmember fixed to the rear end of the motor and having an annular surfaceforming the outer wall of the convergent portion of the nozzle andterminating in a circular opening at the throat of the nozzle, acircular spike member movable axially relative to said opening having afirst portion forming the inner wall of the convergent portion of thenozzle and a second downstream portion forming the inner wall of thedivergent portion of the nozzle, said inner wall of the convergent anddivergent portions being subjected to pressure of the gas, producing afirst force tending to move the spike member forwardly to increase thearea of the throat, the improvements, in combination, comprising:

(a) said spike member having an annular surface, subjected to chamberpressure, of considerably less area than the projected area of saidconvergent-divergent portions, producing a second force tending to movethe spike member rearwardly to thereby decrease the aera of the throat,

(b) an actuator disposed within said spike member and operativelyconnected thereto, so constructed to produce a force in excess of thedifference between said first and second forces, to thereby move thespike member to a desired axial position,

(c) a fixed tube having its forward end secured to a forward bulkhead ofthe motor and its rear end secured to a fixed circular plate.

(d) said spike member having an annular portion surrounding theperiphery of said plate and slideable relative thereto,

(e) said annular portion forming the area upon which said second forceis applied, and

(f) means extending through said tube for controlling the movement ofsaid actuator.

3. A nozzle in accordance with claim 2 wherein,

(g) said first portion of said spike member is cylindrical and slideablydisposed within an annular ring member supported by said cowl member bya plurality of angularly spaced webs.

References Cited UNITED STATES PATENTS 2,570,629 10/1951 Anxionnaz etal. 2,811,827 11/1957 Kress. 3,192,712 7/1965 Nash et al.

SAMUEL FEINBERG, Primary Examiner

1. IN A VARIABLE THROAT AREA CONVERGENT-DIVERGENT NOZZLE OF THEISENTROPIC SPIKE TYPE FOR USE WITH A GASEOUS THRUST MOTOR HAVING A COWLMEMBER FIXED TO THE REAR END OF THE MOTOR AND HAVING AN ANNULAR SURFACEFORMING THE OUTER WALL OF THE CONVERGENT PORTION OF THE NOZZLE ANDTERMINATING IN A CIRCULAR OPENING AT THE THROAT OF THE NOZZLE, ACIRCULAR SPIKE MEMBER MOVABLE AXIALLY RELATIVE TO SAID OPENING HAVING AFIRST PORTION FORMING THE INNER WALL OF THE CONVERGENT PORTION OF THENOZZLE AND A SECOND DOWNSTREAM PORTION FORMING THE INNER WALL OF THEDIVERGENT PORTION OF THE NOZZLE, SAID INNER WALL OF THE CONVERGENT ANDDIVERGENT PORTIONS BEING SUBJECTED TO PRESSURE OF THE GAS, PRODUCING AFIRST FORCE TENDING TO MOVE THE SPIKE MEMBER FORWARDLY TO INCREASE THEARE OF THE THROAT, THE IMPROVEMENTS, IN COMBINATION, COMPRISING